The present invention relates to a radiographic image conversion panel that is irradiated with an exciting light beam to generate a stimulating light beam, and a radiographic image acquisition system using the radiographic image conversion panel. In particular, the invention relates to a radiographic image conversion panel having a position detecting marker of a recorded radiographic image, and a radiographic image acquisition system.
Up to now, a radiographic image recording/reproducing system composed of a radiographic image recording apparatus, and a radiographic image reading apparatus is known as a computed radiography (CR) system, which records a radiographic image of a subject such as a human body on an accumulative phosphor layer once as a latent image, irradiates the accumulative phosphor layer with an exciting light beam such as laser light to generate a stimulating light beam, and photoelectrically detects the stimulating light beam to acquire an image signal representing the radiographic image of the subject, using an accumulative phosphor (stimulable phosphor) that is irradiated with a radiation such as an X-ray to accumulate a part of the radiation energy, and then, is irradiated with an exciting light beam such as visible light to exhibit stimulating light-emission in accordance with the accumulated radiation energy.
As a recording medium used in the radiographic image recording/reproducing system, a radiographic image conversion panel produced by stacking an accumulative phosphor layer on a substrate is used. The radiographic image conversion panel releases remaining radiation energy when irradiated with an erasing light beam to become capable of recording a radiographic image again. Thus, the radiographic image conversion panel can be used repeatedly.
The radiographic image conversion panel used in the above-mentioned radiographic image recording/reproducing system is acquired in such a manner that the accumulative phosphor layer as a recording layer is formed on a support by a method such as vapor-deposition to produce a phosphor sheet, and then the phosphor sheet is placed in a package, such as moisture proof package, which is then formed into a panel. For the radiographic image conversion panel thus formed, it is important to be free from major structural defects that result from vapor-deposition unevenness of the accumulative phosphor layer during the vapor-deposition step. Needless to say, if the defects are negligible, they do not influence diagnosis. However, if the defects are at a predetermined level or higher, they influence diagnosis, and therefore it is necessary to perform some countermeasures against the defects before using the radiographic image conversion panel having such level of defects.
Further, as the above-mentioned radiographic image reading apparatus, for example, an apparatus is known, which includes a line sensor for detecting a stimulating light beam generated from a radiographic image conversion panel when irradiated with a linear exciting light beam, and transfer means for transferring the line sensor relatively in a direction orthogonal to the direction of the linear exciting light beam with respect to the radiographic image conversion panel, and is irradiated with the linear exciting light beam to detect the stimulating light beam generated from the radiographic image conversion panel, while transferring the line sensor relatively with respect to the radiographic image conversion panel, thereby acquiring a radiographic image.
The radiographic image acquired as described above is subjected to shading correction or the like for removing the influence of light-emission unevenness by the stimulating light beam, and is recorded on a film as a visible image or displayed on a high-precision CRT, thereby being used for diagnosis.
As a technique related to the shading correction used herein, for example, the following is known: a radiographic image (i.e., a radiographic image for correction) read from a radiographic image conversion panel that is uniformly exposed to a radiation (hereinafter referred to as uniform exposure, or solid exposure) is stored previously in an apparatus, then, a radiographic image (i.e., a radiographic subject image) read from the radiographic image conversion panel exposed to a radiation through a subject is acquired, and the radiographic image for correction is subtracted from the radiographic subject image to acquire a radiographic image (corrected radiographic image) with the influence of shading removed (for example, see JP 2000-013599 A and JP 64-086759 A).
However, according to the above technique, the variation in the arrangement position of the radiographic image conversion panel on the radiographic image recording apparatus and the radiographic image reading apparatus when the radiographic image for correction is recorded is not considered, which causes a problem in that a positional displacement error is not corrected.
In order to solve the above problem, the applicant of the present invention has proposed a technique of performing a position correction regarding the shading correction in Japanese Patent Application No. 2002-279248 “Radiographic image acquisition method and apparatus” (see JP 2004-117684 A).
According to this technique, a light-emitting marker for specifying the position on the radiographic image conversion panel is placed outside of a main image area of the radiographic image conversion panel, and the position specified by the light-emitting marker is read, whereby the position of the radiographic image conversion panel itself is specified.
More specifically, the technique disclosed by JP 2004-117684 A, is based on the idea that the transfer positional displacement of the radiographic image conversion panel is corrected at a time of recording, and after the transfer positional displacement is corrected, a predetermined correction (such as shading correction or other corrections for removing the influence of light-emission unevenness) is performed. In this technique, the light-emitting marker for specifying the position on the radiographic image conversion panel is placed outside of a main image area of the radiographic image conversion panel, whereby the convenience of a correction operation and the reliability of correction results higher than those in the previous techniques can be obtained.